Though I have had System Restore work some of the time, it is generally so unreliable that I have a hard time actually counting on it to work right when I really need it to.
A much more reliable, though manual, system is to use Norton Ghost and either a second hard drive, or a second partition. Then I just make a Ghost copy of the System drive/partitioin before I do any major changes or try new software, or once a month. It takes less than 10 minutes, and if you like, you can burn CDs or DVDs with it or a permanent archive.
Let me tell you, as a professional software reviewer, Ghost makes rolling your computer back to an earlier version fast and simple, and very reliable.
-Llama